> > > > > I did some S3 tests on an eeepc901, the total suspend time(from issue > > > > > the suspend command to power down) is about 2.5s~3s. > > > > > something interesting is that kernel runs disk sync before entering S3 > > > > > state, and this takes about 0.7~1.2s. > > > > > my question is that, why do we need this for s2ram? > > > > > can we remove this and run sys_sync for S4 only? > > > > > > > > At the risk of sounding foolish, I'd guess that a system in S3 (or more > > > > generally, suspend-to-RAM) is a lot more at risk of losing power or > > > > failing to restore than a normally running system. (A normally running > > > > system is trivially not at risk of failing to restore!) Consequently > > > > it makes sense to flush the I/O buffers before entering this state, to > > > > minimize the potential for loss of data. > > > > > > > > When you think about it, a system in S4 is actually _less_ likely to > > > > run into trouble than one in S3, since it can't fail because of loss of > > > > power. So if anything, we should remove the disk sync from hibernation > > > > and leave it in system suspend. > > > > > > I generally agree, but I think we may also leave the syncing to the user space, > > > in both cases. > > > > Well... > > > > Normally kernel writes dirty data to disk each 30 > > seconds. s2ram/s2disk breaks that promise, so it seems fair to add > > explicit sync to keep the "promise". > > > > OTOH, I agree it would be more flexible if we left sync to > > userspace. In uswsusp case, it actually makes sense. In s2ram > > case... if we can do it while keeping compatibility with old > > behaviour... why not. > > That really depends on the distrubution. (open)SUSE always syncs before > suspend/hibernation AFAICS, but I don't know about the other distros. At least I ran into habit of running "echo mem > /sys/power/state" manually on zaurus. I guess nontrivial ammount of people have custom scripts that may or may not sync... Anyway, if distro already ran sync, additional one is likely to be very fast. Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
